[Ri...] Posted December 4, 2020 Share Posted December 4, 2020 Please take a look at the attached drawing, and provide feedback. Is the MMB on Datum D valid? Link to comment Share on other sites More sharing options...
[Ri...] Posted December 4, 2020 Author Share Posted December 4, 2020 GOM does some weird things when I try to throw the MMB on. Link to comment Share on other sites More sharing options...
[Da...] Posted December 4, 2020 Share Posted December 4, 2020 ASME Y14.5-2018 doesn't allow it: Please sign in to view this quote. Link to comment Share on other sites More sharing options...
[Ri...] Posted December 4, 2020 Author Share Posted December 4, 2020 Thank you for the information, Daniel. Link to comment Share on other sites More sharing options...
[Da...] Posted December 4, 2020 Share Posted December 4, 2020 I think it will be the same in ISO, unfortunately I don't have the ISO 2692 handy, where it should be found. Or whatever standard, in ISO it's not easy to keep track of what is where. Link to comment Share on other sites More sharing options...
[He...] Posted December 5, 2020 Share Posted December 5, 2020 Please sign in to view this quote. I'm not sure that 2 parallel planes will qualify as a planar datum. ASME is very functional and in theory I see no reason why it shouldn't be allowed. But in this case the effect is more or less negligible since the axis direction of the holes is the same as the normal of the datum. Link to comment Share on other sites More sharing options...
[Ma...] Posted December 7, 2020 Share Posted December 7, 2020 We take datum D as plane symetry - so i think that MMB can not be used. Just talking loud Link to comment Share on other sites More sharing options...
[Ja...] Posted December 7, 2020 Share Posted December 7, 2020 MMB is valid on datum feature D if we are working to Y14.5. The datum is the width, or two parallel planes, so it is a feature of size and the MMB reference is valid. ISO 2692 - 2006 states in 4.2.2 NOTE 1 that the modifier is allowed on the datum reference if the datum is obtained from a feature of size. The datum label is attached to the width dimension, so I would assume that it is obtained from a feature of size and thus the modifier is allowed, but I am not fluent in ISO. Link to comment Share on other sites More sharing options...
[Ja...] Posted December 7, 2020 Share Posted December 7, 2020 Please sign in to view this quote. Daniel, datum D is not planar, it is the width formed by the two external parallel planes. Link to comment Share on other sites More sharing options...
[Ke...] Posted December 7, 2020 Share Posted December 7, 2020 Please sign in to view this quote. Bus isn't Datum D the width *and* the symmetry plane? If so, would one supercede the other? Link to comment Share on other sites More sharing options...
[Ja...] Posted December 7, 2020 Share Posted December 7, 2020 Please sign in to view this quote. I guess we have to be careful with our wording. I didn't word it properly. The datum feature is the width. The datum is the center plane. Material modifiers are applied to datum features. Thus, the MMB modifier would be applied to the width which is valid per Y14.5. Link to comment Share on other sites More sharing options...
[Ri...] Posted December 7, 2020 Author Share Posted December 7, 2020 Well now I'm even more confused. If the ASME 7.11.3 isn't valid for this notation, then please show me an example of what it is referring to. I'm struggling to understand how Datum D isn't a Planar feature. Link to comment Share on other sites More sharing options...
[Ma...] Posted December 7, 2020 Share Posted December 7, 2020 Datum D is a variable width created between two planar features. It will be a perpendicular in Calypso, ala the theoretical circle MMC method, not a symmetry plane. The 'other' software has 'width as datum' functionality. Link to comment Share on other sites More sharing options...
[Ri...] Posted December 7, 2020 Author Share Posted December 7, 2020 Please sign in to view this quote. Wait, there is a difference between Symmetry, and Symmetry Plane. Symmetry Plane is there for cases like this. It is one feature created from two parallel planes that is a feature of size. Link to comment Share on other sites More sharing options...
[Ja...] Posted December 7, 2020 Share Posted December 7, 2020 Please sign in to view this quote. I assume you are using Y14.5-2018. Look at Figure 7-3. Feature type (a) is a planar datum feature and the datum is a plane. Feature type (b) is a width datum feature and the datum is a (center) plane. In both rows, the datum is a plane. The datum feature, however, is different. One (width) is a feature of size, the other (plane) is not. A datum feature can be referenced at MMB if it is a width, not a plane. Link to comment Share on other sites More sharing options...
[Ma...] Posted December 7, 2020 Share Posted December 7, 2020 Please sign in to view this quote. Yes, but the symmetry plane will be parallel to the outer parallel planes and not oriented correctly for the expanding/contracting width. Link to comment Share on other sites More sharing options...
[Ri...] Posted December 7, 2020 Author Share Posted December 7, 2020 Please sign in to view this quote. OK. I looked over these, and I understand where the confusion comes from. So since it appears that it is legal, it appears that Calypso clearly cannot handle this, and I'm not certain of a workaround. I'm even more confused as to what the GOM software is doing because with MMB turned off it appears to build the DRF correctly, but with it turned on it makes a really weird axis plane. Link to comment Share on other sites More sharing options...
[Ri...] Posted December 7, 2020 Author Share Posted December 7, 2020 Please sign in to view this quote. I'm not certain that I agree with that. Link to comment Share on other sites More sharing options...
[Da...] Posted December 7, 2020 Share Posted December 7, 2020 If plane 1 is cut .005 small and plane 2 is .005 long, the width is still nominal but the centerline is shifted. Link to comment Share on other sites More sharing options...
[Ja...] Posted December 7, 2020 Share Posted December 7, 2020 Please sign in to view this quote. Something seems a bit off in the GOM software. From your images, GOM states that datum reference frame (DRF) [D|A|B(M)] is fully constrained (no remaining degrees of freedom (DOF)). It isn't quite "fully" constrained but rather "partially" constrained with the MMB modifier on datum feature B partially freeing one translational DOF (the only DOF that B is allowed to constrain). As soon as you add the MMB modifier on datum feature D for DRF [D(M)|A|B(M)], GOM states that there are 2 translations and 1 rotation free. Datum feature D will constrain two rotational DOF and one translational DOF, datum feature B will constrain one translational DOF. That being said, DRF [D(M)|A|B(M)] should be partially constrained with 2 rotational DOF and 2 translational DOF partially free. This may be a subtle difference between MMR (ISO) and MMB (ASME) that I can't quite speak to. As far as ASME is concerned, GOM doesn't seem to be correct. Link to comment Share on other sites More sharing options...
[Ri...] Posted December 7, 2020 Author Share Posted December 7, 2020 Please sign in to view this quote. When you build DRFs in GOM it doesn't give you the option of selecting ASME or ISO, but when you actually evaluate the Position it allows you to select ASME or ISO. It's weird. Yes though, I saw what you are talking about. If you notice when MMB is select for Datum D look at the Datum D plane that it creates which makes no sense. Lol. It's probably a bug that I'll bring up to the GOM experts - I just thought that I'd share that. I have another software that I'm going to try to do some testing on to see if I can test this example of a Position callout. If anyone has a machine with PC-DMIS I'd be interested in seeing how it handles this. Link to comment Share on other sites More sharing options...
[Ja...] Posted December 7, 2020 Share Posted December 7, 2020 I'm curious to hear what GOM says about it. See the following images for the result in PC-DMIS. As you can see, there is no mention of "datum shift" when I have [D|A|B] because the DRF is fully constrained. When I have [D|A|B(M)], you can see the datum shift table appear and one translational DOF is partially free (not fixed). When I have [D(M)|A|B(M)], you can see two rotational DOF and two translational DOF appear partially free. This matches the "theory" and the directions line up with the way that I aligned the example part. Everything seems to be in working order. Link to comment Share on other sites More sharing options...
[Ri...] Posted December 7, 2020 Author Share Posted December 7, 2020 Jacob, Thank you for your assistance. Looks like another loss for Calypso in this area. 🙁 Link to comment Share on other sites More sharing options...
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